The present invention relates to the use of a catalyst preparation system for the preparation of a diluted catalyst slurry. In particular, the invention relates to a catalyst preparation system comprising a mixing vessel for mixing a particulate catalyst and a liquid hydrocarbon diluent. According to the invention, diluted catalyst slurry is prepared in a mixing vessel comprising a rotatable axial impeller system comprising at least two double-bladed hubs. The invention also relates to a process for preparing diluted catalyst slurry for use in the preparation of a particulate polyethylene product in a loop reactor with the catalyst preparation system as described herein.